[exim] Shared Hosting + Specific Domain outbound filter

Hi All,

I have a CPanel server that uses Exim as it's MTA.
I have multiple domain names on this server all using email.

My customer has signed up for an email encryption service from
Barracuda so I now need to make / create an outbound filter but it
needs to be specific from that one sending domain and not globally
from all domains.

Example:

*@customer.com > Subject: encrypt > forward to the Cuda smart host
that will handle encryption based on subject

*@customer.com > Subject: anything else here > goes out the door from
the CPanel server

*@othercustomers > Subject: anything here too including "encrypt" >
goes out the door from CPanel server like it always has

I'm not quite sure after looking at forums, etc how to do this. I
know I need to use a "router" function but how to lock it down to
individual domain names for outbound filtering I'm just not certain
and I can't figure out what I should do or where.

Any help or guidance would be much appreciated.

Thanks!